1. Technical Field
The present invention relates to a threading attachment for internal or external threading which includes a spindle head that is intended to be attached to a spindle on a machine tool, and also a tap holder in which a tap is arranged during the threading work. The tap may, for example, be a tap for internal threading of holes or a die for external threading of a bar. The invention also relates to a threading method.
2. The Prior Art
For internal threading of holes by means of known threading attachments, the threading attachment is attached to a spindle on a machine tool and is also connected to a firm part of the machine tool via a protruding arm. The threading attachment includes a spindle head in which a tap holder is placed to support a tap and to cause the tap holder and the tap to rotate during the feed motion into the hole to be threaded when the spindle head is rotating. When the tap has reached the required depth of thread, the feed motion will be stopped and changed into an outfeed motion, the tap holder via a planetary gearing in the spindle head being brought to rotate in the opposite direction and to thread the tap out of the hole during the outfeed motion. In order to make this reversed direction of rotation possible, it is necessary to fix the position of the planet wheels in relation to the machine tool with the above-mentioned protruding arm.
Because of their construction, the known threading attachments of the kind mentioned above are expensive to produce and to some extent sensitive to interruption of the service. For that reason there is a requirement to achieve threading attachments which are both more inexpensive to produce and more reliable in running than the prior known threading attachments.